1. Field of the Invention
The technical field of the present invention relates to a display device and a driving method thereof. Further, the technical field of the present invention relates to a semiconductor device and a driving method thereof.
2. Description of the Related Art
In recent years, a display device provided with a display panel having a photosensor has attracted attention.
The amount of light which reaches a display panel changes when an object is in contact with or approaches the display panel. A photosensor detects change in the amount of light; accordingly, contact or approach of the object can be detected.
As an example of such a display device, a display device equipped with an image capturing function by providing a contact area sensor for a display panel is given (for example, see Patent Document 1). Further, as an example of a device without a display panel, a semiconductor device such as an image sensor can be given.
In the display device, an image is captured as follows. When an object is in contact with or approaches the display panel, light is emitted to the object from the display panel, and part of the light is reflected by the object. A photosensor is provided for a pixel of a display panel, and detects the reflected light and converts it into electrical signals so as to obtain image data; thus, an image is produced.
For capturing an image with high precision, reduction in noise caused by variations in characteristics of photosensors provided in pixels of a display panel is required. Due to the noise, a defective pixel in which an intended image can not be formed exists.
A technique to correct image data of the defective pixel is known (for example, see Patent Document 2).